Multi-stage bubble column humidifier apparatus

ABSTRACT

A downcomer apparatus for use in a multi-stage bubble column humidifier. The humidifier comprises at least a first, second and third stage, wherein each of said stages includes an inlet, an outlet and a chamber defined by said stage, in fluid communication with the inlet and the outlet. In the humidifier, a heated liquid fluid stream flowing downwardly exchanges mass and heat with a cooler carrier gas stream flowing upwardly through the bubble column. A bubble generator comprising a perforated plate, or sparger, passes the carrier gas, such as air, from a lower chamber to form bubbles in a fluid, such as water, forming a bath on an upper chamber. An off-set arrangement of downcomer apparatuses, wherein said apparatus comprises a funnel, a watergate, and a downcomer, is used to prevent a recirculation of humid bubbles from the upper chamber to the lower chamber, thus preventing the air stream from circumventing the bubble generator in the form of the humid bubbles. This arrangement assures the maximum possible performance of the humidifier, as the entire air stream is forced to move through the bubble column, thus maximizing the air-water surface interface for an efficient mass and heat exchange.

FIELD OF THE INVENTION

A multi-stage bubble column humidifier apparatus comprising a downcomerunit. A multi-stage bubble column humidifier apparatus comprising adowncomer unit for use in a humidification-dehumidification system forpurifying a liquid, such as water.

BACKGROUND OF THE INVENTION

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

As explained in the “Special Report on Water” in the 20 May 2010 issueof The Economist, in this century, a shortage of fresh water may surpassa shortage of energy; and these two challenges are inexorably linked.Despite an increased focus on this issue, many subsequent reports,including the World Health Organization's “2014 Update on the Progressof Drinking Water and Sanitation”, describe the uneven and unequalprogress being made towards achieving fresh water supply goals.

Current estimates indicate that approximately 748 million people stilllack access to an improved drinking water source. Of these, almost aquarter (173 million) rely on untreated surface water. Markedly, thediscrepencies in accessing improved sources of drinking water corresponddirectly with geographic, sociocultural and economic inequalities.

The hazards posed by an insufficiency and/or incontinuity in the supplyof clean water are particularly acute. Continuity of a water supply istaken for granted in most industrialized countries, but is of greatconcern in many developing countries. Recent estimates indicate thatapproximately half of the population of developing countries receivewater on an intermittent basis, such as water being provided for a fewhours per day, or a few days per week. Further still, the supply offresh water is often seasonally inconsistent. Global warming, and anyclimate changes brought about, may further threaten these regions.

Understandably, an insufficient and/or intermittent supply of freshwater may lead to a variety of crises, including famine, disease, death,forced mass migration, cross-region conflict/war, and collapsedecosystems. Despite the crucial need for fresh water, supplies of thisliquid are nonetheless constrained.

Although nearly 70% of the Earth's surface is covered by water, 97.5% issaline and ocean-based. Of the remaining 2.5% (fresh) water, only 1% iseasily accessible, i.e. found in underground aquifers. Adding to globalshortages of fresh water is the fact that the distribution of freshwaterthat is easily available is vastly unequal. According to the WorldBusiness Council for Sustainable Development, more than half of thenaturally-occurring fresh water supply is contained in regional drainagebasins located in just nine countries (United States of America, Canada,Colombia, Brazil, Democratic Republic of Congo, Russia, India, China andIndonesia).

As the world's population escalates, a consequential shift in farmingand industrialization occurs in order to support this growing number ofpeople. These shifts further intensify the demands for clean, freshwater. Urban areas have a greater need for water beyond the basics fordrinking and sanitation. As naturally occurring fresh water is typicallyconfined to regional drainage basins, transport of fresh water to urbanlocalities must be undertaken with ever-increasing costs.

Summarily, these increases in urbanization and population, as well asglobal warming, all have an impact on the environment, and contribute tothe ecological consequences of drying reservoirs and falling aquifers.The resultant fresh water shortages necessitate methods of obtainingfresh water from non-fresh water sources such as, but not limited to,seawater, brackish water and/or even waste water.

In light of this issue, a number of apparatus have been developed toovercome fresh water shortages. These devices operate by separating purewater from a feed liquid selected from the group consisting of, but notlimited to, seawater, brackish water and/or waste water. The term wastewater includes flowback water and water produced during an oil or gasextraction/production process.

Flowback water or “backflow” water is further defined as a fracturingfluid mixture obtained after an extraction process (recovered fracturingfluid and produced water). It is also known as the recovered water andfracturing fluid which flows back from an oil or gas well drillingfracturing process. Both the fracturing chemicals and fresh water thatis injected into the well during the fracturing process tend to dissolvesalts in the rock formation, thus increasing the salinity of theflowback water. As such, flowback waters are typically high in salinityand total dissolved solids (TDS), and comprise from about 10-60% percentof the volume of fluid that was initially injected into the well.Flowback waters can also contain contaminants that are present in a rockformation undergoing a fracturing process.

Although there are many existing processes for producing fresh waterfrom seawater brackish water, and/or waste water, the majority of themrequire massive amounts of energy. For example, despite being thecurrent leading desalination technology, reverse osmosis (RO) is energyintensive and still relatively inefficient due to the high pressurerequired to drive water through membranes and their tendency to foul. Inlarge-scale plants, the specific electricity required can be as low as 4kWh/m³ at 30% recovery, as compared to the theoretical minimum of around1 kWh/m³; while smaller-scale RO systems (e.g., aboard ships) are evenless efficient.

Other existing seawater desalination systems include athermal-energy-based multi-stage flash (MSF) distillation process, and amulti-effect distillation (MED) process; both of which are energy- andcapital-intensive. Furthermore, in the MSF and MED systems, the maximumbrine temperature and the maximum temperature of the heat input arelimited so as to avoid calcium sulphate precipitation, which leads to aformation of a hard scale on the heat transfer equipment. As such, whenthese technologies are employed, they are usually done on a large scaleand are mainly suitable for those economically advanced andresource-rich regions of the world, as many developing countries lacksufficient energy resources to carry out these methods.

One solution is to develop small-scale desalination technologies whichcan utilize solar energy. Humidification-dehumidification (HDH)desalination systems, are considered advantageous alternatives inproviding low to medium scale water production for remote and off-gridareas, and thus provide a promising technology to resolve the issue offresh water scarcity.

Key components of the HDH desalination systems include a humidifier, adehumidifier, a compressor and an expander. They are also considered tobe the same key components in a basic varied-pressure HDH desalinationcycle; one of the many configurations of HDH desalination cycles. Ofthese components, the heat and mass transfer devices (humidifier anddehumidifier) play a major role in the HDH systems, and use a carriergas, such as air, to communicate energy between a gas and a liquid, suchas a seawater brine. In the humidifier, hot seawater comes into directcontact with dry air, and this air becomes heated and humidified. In thedehumidifier, the heated and humidified air is brought into (indirect)contact with cold seawater and gets dehumidified, producing pure waterand dehumidified air.

In light of fresh water demands, efficient, high-performancehumidification dehumidification desalination (HDH) systems arenecessitated. Those systems comprising a low-cost humidifier possessingan efficiency rating of 85±5% are greatly preferred, as the overallefficiency of the HDH system will also be directly increased.

There are several devices that could be used as a humidifier for the HDHsystems. These devices include, but are not limited to, packed bedtowers, spray towers, wetted-wall towers, and bubble columns. [R. E.Treybal Mass transfer operations. 3^(rd) edition New York: McGraw-Hill1980 Incorporated herein by reference in its entirety.]

In a spray tower, water is sprayed at the top of a cylindrical columnand falls in the form of droplets—due to gravity—while a running airstream flows upward, so as to be in direct contact with the waterdroplets. Mist eliminators are essential in this situation, so as toavoid water entrainment in the air leaving the column. These types ofhumidification devices have a low effectiveness due to their low waterhold up. Moreover, the pressure drop in the water stream is high due tothe losses in the spray nozzels. [F. Kreith and R. F. Bohem;Direct-contact heat transfer. Washington: Hemisphere Pub. Corp., 1988Incorporated herein by reference in its entirety.]

As for wetted-wall towers, these devices suffer from a low water flowrate capacity since the water only flows on the inner surface of thetower, and they are not preferred. Conversely, the packed bed tower iswidely used as a humidifier in HDH systems [Said Al-Hallaj, MohammedMehdi Farid, and Abdul Rahman Tamimi. “Solar desalination with ahumidification-dehumidification cycle: performance of the unit”.Desalination 120.3 (1998), pp. 273-280. Y. J. Dai, R. Z. Wang, and H. F.Zhang. “Parametric analysis to improve the performance of a solardesalination unit with humidification and dehumidification”.Desalination 142.2 (2002), pp. 107-118.93. A. S. Nafey, H. E. S. Fath,S. O. El-Helaby, and A. Soliman. “Solar desalination usinghumidification-dehumidification processes. Part II. An experimentalinvestigation”. Energy Conversion and Management 45.78 (2004), pp.1263-1277. Ghazi Al-Enezi, Hisham Ettouney, and Nagla Fawzy. “Lowtemperature humidification dehumidification desalination process”.Energy Conversion and Management 47.4 (2006), pp. 470-484. G. PrakashNarayan, Maximus G. St. John, Syed M. Zubair, and John H. Lienhard V:“Thermal design of the humidification dehumidification desalinationsystem: An experimental investigation”. International Journal of Heatand Mass Transfer 58.12 (2013), pp. 740-748.11-15. Incorporated hereinby reference in their entirety.] However, in some operations, the fluidpassing through the packed bed may contain suspended solid particlesthat can accumulate on the packing material and cause a reduction in thegas-liquid volumetric flow rates and, in extreme cases, a plugging ofthe tower. Therefore, alternative methods to using a packed bed towerare desired.

Recently, bubble columns have received much consideration as such analternative to packed bed towers [(G. P. Narayan, M. H. Sharqawy, S.Lam, J. H. Lienhard V, and M. St. John. “Multistage bubble columnhumidifier”. Pat. Application Publication No. US 2014/0367871.Incorporated herein by reference in its entirety.] In a simplisticbubble column humidifier, hot water enters into the bubble column andaccumulates until it reaches a certain level while air is concurrentlyinjected into the column through a perforated plate or perforated pipe(sparger) located at the bottom of the column. This results in theformation of bubbles in the pool, or bath of accumulated hot water. Inan alternative embodiment, bubble columns comprise upright columnsprovided with a multiplicity of spaced-apart stages each provided with aporous structure, sometimes referred to in the art as a bubble generatoror bubble distributor.

Porous structures commonly used in these apparatus include those such assieve plates and/or spargers comprising openings that can be describedas pores, holes, or perforations. It is through these openings that aflowing stream of gas is passed so as to contact with a liquid streambeing generally conveyed downwardly, and in cross-current flow, fromstage to stage so as to maintain a substantially continuous phase. Suchapparatus are commonly used to treat waste water or sea water in orderto obtain pure or fresh water.

During a vapor-liquid contact process, such as a humidification process,if a pressurized gas is forced into a liquid through a fine network ofopenings in a porous structure, small diameter bubbles of the gas areformed in the liquid, resulting in a foam, or froth. This froth aids inthe transfer of heat from the water to the gas. The smaller the bubbles,the higher the ratio of the carrier gas to the feed liquid so as topermit a greater efficiency in the mass and temperature transfer betweena carrier gas and a feed liquid.

Previously, drilled porous plates, or spargers, possess openings thatproduce larger bubbles. As these bubbles do not as readily absorb aliquid component in vapor form, it is necessary to find those porousstructures that can generate finer bubbles. Smaller bubbles increase thesurface area to volume ratio and, therefore, speed up the mass and heattransfer reaction rates to save valuable processing time. Some porousstructures have a ‘nozzle-like’ design, wherein the openings on thelower, or gas entrance side, are greater in diameter when compared totheir respective openings on the upper, or gas exit side. This designprovides a pressure advantage, and, if a lower internal pressure occurs,the finer pore openings (smaller diameter) are also used to prevent anyliquid from penetrating back into the pores.

Although the finer pore size may favor the exchange of mass and heatbetween the cross flow streams, other factors including, but not limitedto, the integrity of the porous structure and the amount of solids foundin the liquid stream, should be considered when choosing a porousstructure for a humidifier apparatus. It is noted that the smaller theporous openings, the greater risk of fouling of the openings bysediments, salts and other contaminants found in a feed liquid. Porousstructures having too great of a total porous surface area often sufferfrom cracking, or breaking, with increased gas pressure stresses.

Further to mass and temperature transfer, this interchange by directcontact between a liquid, such as water, and a gas, such as air, iseffected by causing the gas to bubble through a thermal layer, or layersof the liquid. The air bubbles, as they enter from a lower vantage pointand pass through the water bath on each stage, provide for a largersurface area of contact between the gas and the heated liquid (to becooled). The effect of such an arrangement is that the air streams orbubbles that form are continuously distorted and become subject toturbulence which is created as they pass through the much denser thermallayer or layers of the liquid bath. The result of this turbulence isthat the interior of the air bubbles and air streams are brought to theinterface of a cooler gas and a warmer liquid, and thereby heat transferis promoted (achieved). Mass exchange occurs when the gas, nowhumidified, carries with it a percentage of steam, or water. Theremaining liquid is now more concentrated than when it entered thehumidifier apparatus, i.e. by having attained a higher concentration ofa solute such as, but not limited to, minerals, salts, waste componentsand/or mixtures thereof. Systems that create air bubbles in water arefound to be advantageous in mass and temperature transfer over thosesystems that created fine droplets of thin films of water.

Theoretically, to maximize the efficiency of mass and temperaturetransfer, all of a gas stream introduced to a multi-stage bubble columnhumidifier flows upwardly so as to pass through a series of liquidbaths, each held in their respective chamber, until the gas reaches anuppermost section of an uppermost chamber and flows through—in itsentirety—into the atmosphere, or into a capturing device held thereon.As stated, it is within this cross-current flow configuration that massand heat transfer coefficients are maximized due to a diffusion of water(in the form of a vapor, or steam, component) into the bubbles of gas.Key to this transfer is the formation of a foam or ‘froth’ at thelocation where the air bubbles are dispersed throughout the water withinthe chamber(s) of the bubble column humidifier. The froth, by increasingthe surface area for mass and heat transfer, also increases the rate ofthis transfer reaction.

Any impediments to the bubble formation process will directly impact thelevel of foam formation. For example, the central placement of adowncomer unit in previous vapor-liquid contact apparatus restrictedvaluable bubble distributor, or sparger, space. Also, seen in previousapparatus, the release of a liquid stream from a liquid bath held on onestage directly on top of the foam forming in an adjacent underlyingchamber dampened the froth, or foam, formation.

However, although the presence of foam increases the rate of mass andheat transfer, the overall efficiency of the bubble column humidifierwill decrease if the foam (bubbles) are allowed to return to apreceding, or prior, chamber. Therefore, an overproduction of foam isnot preferred. In previous apparatus, high levels of foam resulted inthe direct entry of bubbles into downcomer units so as to be transportedto adjacent underlying chambers, thus reducing efficiency. Furthermore,if a high level of foam contacts the porous plate of the adjacentoverlying chamber, this may result in a bursting of the bubbles andrelease of the vaporizable component, thus also reducing efficiency.

Therefore it is desirable to have a means for controlling anover-formation of foam, and for preventing the return of any bubblecomponent to a previous chamber. As foam formation is mainly influencedby the air superficial velocity and the height of any water gatesinstalled in a liquid-vapor contact apparatus, such as the bubblehumidifier apparatus, a means for controlling this component isimportant. Having a watergate that is easily adjusted is an importantfactor.

A downcomer unit can be used as a watergate. Downcomer units may becontiguous with the humidifier vessel itself. If the downcomer unit iscontiguous with the exterior shell of the bubble column humidifier, thewatergate, or any part of the downcomer, may not be easily adjusted norreplaced in case of breakage. Additionally, the height of the water gateis not only important for foam formation, but also for liquid transferconcerns. Truncated water gate designs have several inherentlimitations. For example, the water gate may not provide a sufficientlength so as to cause the fluid in the chamber below to back up into thewater gate. This will impede the flow of the liquid, and may even causeit to re-enter the chamber from which it originated. Also, any watergate releasing its contents at a location above the water bath increasesthe probability of sediments from the liquid, such as salts fromseawater, accumulating on the porous structure. This may foul theopenings of the porous structure, such as a sparger, so as to impede theflow of a gas, such as air, and reduce the efficiency of the apparatus.If the efficiency of a humidifier is compromised, the overall efficiencyof a HDH system will also suffer, and thus limit the delivery ofpurified water.

Recent research has been directed to the development of an effectivehumidifier. For example, an approach as disclosed in U.S. Pat. No.6,919,000 provides a reduction in the thermal resistance associated withincondensable gases by using a direct-contact condenser instead of astandard, indirect contact dehumidifier. This method increases the heattransfer rates in the condenser at the expense of energy efficiency, asthe energy from the humid air entering the dehumidifier is not directlyrecovered to preheat the seawater. Thus, although the cost of thedehumidification device is reduced, the energy costs associated withthis method actually increase.

Another alternative approach as disclosed in U.S. Pat. No. 4,045,190provides a method for regulating the flow of liquid through masstransfer columns using throttle valves responsive to a gas pressure dropor a height of a liquid. However, some bubbles may leave with the waterstream; subsequently reducing the heat recovery in the humidificationprocess.

Further to this approach, U.S. Pat. Nos. 6,250,611 and 6,575,438 bothdescribe vapor-liquid contact apparatus for use in carrying out chemicalprocessing which use downcomer(s) fixed with a sparger plate. However,in these two references, it is not possible to adjust the height ofwater level, and, most significantly, numerous bubbles may leave withthe water stream.

A simple, low cost vapor-liquid contact apparatus, such as a multi-stagebubble column humidifier apparatus, providing a means to limit the loss,or return, of a vapor component so as to achieve an increased efficiencyin mass and/or heat transfer, is greatly desired.

SUMMARY OF THE INVENTION

The present disclosure relates to a multi-stage bubble column humidifierapparatus comprising a downcomer unit for use in a humidificationprocess to humidify a gas stream. Also, the multi-stage bubble columnhumidifier apparatus may be used in a humidification-dehumidificationsystem for purifying a liquid such as water. Herein, the term‘multi-stage bubble column humidification apparatus’ is synonymous withthe term ‘multi-stage bubble column humidifier apparatus’.

According to a first embodiment, the present disclosure is directed to amulti-stage bubble-column humidification apparatus comprising:

-   -   an external shell defining an interior region;    -   a plurality of horizontal porous structures defining vertical        chambers within the interior region;    -   a carrier gas inlet;    -   a carrier gas outlet;    -   a liquid remnant outlet comprising a discharge siphon system;    -   a feed liquid inlet; and    -   a series of downcomer units wherein each pair of vertically        adjacent chambers is in liquid communication via at least one        downcomer unit;    -   wherein the vertical chambers within the interior region        comprise at least a lowermost proximal chamber, an uppermost        distal chamber and at least one mid-chamber between the proximal        and distal chambers,    -   the lowermost proximal chamber comprises:        -   the carrier gas inlet; and        -   the liquid remnant outlet,    -   the uppermost distal chamber comprises:        -   the feed liquid inlet; and        -   the carrier gas outlet,    -   each downcomer unit comprises:        -   a funnel;        -   a watergate;        -   a base cup downcomer;    -   wherein    -   a lower portion of the watergate is seated in the base cup        downcomer and an upper portion is coupled with the funnel.    -   In a further embodiment, the external shell comprises:        -   a column;        -   an upper plate; and        -   a lower plate;    -   wherein the upper plate and the lower plate are sealed to the        column by means of an embedded O-ring.

In a further embodiment, the funnel and the watergate are not contiguouswith the external shell.

In a further embodiment, the porous structure is configured to seal thewater gate therein.

In a further embodiment, the seal comprises an O-ring, configured toprovide an ease of adjustment or replacement.

In a further embodiment, either the porous structure of a distal ormid-chamber, or the bottom plate of the proximal chamber is configuredto seal the base cup downcomer therein, so as to provide an ease ofreplacement.

In a further embodiment, the seal comprises an O-ring configured so asto provide an ease of adjustment or replacement.

In a further embodiment, the base cup downcomer terminates at a pointbelow a level at which a feed liquid or liquid remnant accumulates inany of the proximal, distal or mid chambers.

In a further embodiment, the base cup downcomer is configured todistribute the feed liquid or liquid remnant to any of the proximal,distal or mid chambers in an even-flowing pattern.

In a further embodiment, the base cup downcomer is configured to collecta sediment fraction of a feed liquid or a remnant liquid enteringthrough the feed liquid inlet, or entering through the downcomer unit,so as to prevent or reduce a fouling of the porous structures.

In a further embodiment, the liquid discharge siphon system isconfigured so that no gasses exit with the remnant liquid.

In a further embodiment, the chambers are configured to each have awidth defined by the external shell, measured horizontally, and a heightdefined by the external shell, measured vertically, where the width isat least twice as great as the height.

In a further embodiment the water gate is configured so as to lengthenor shorten a passageway for liquid communication between verticallyadjacent chambers.

In a further embodiment the funnel is configured to limit or eliminatean entrance of a foam or bubble component into the water gate.

In a further embodiment the plurality of porous structures is selectedfrom the group consisting of a sieve plate, a radical sparger, a ringsparger, a spider sparger, and a wheel-type sparger.

In a further embodiment the plurality of porous structures comprise alower porous surface and an upper porous surface wherein the lowerporous surface comprises openings greater in diameter than the upperporous surface.

In a further embodiment the downcomer units are arranged along aperiphery of the distal, mid, and proximal chambers in a vertical,offset pattern, or juxtaposed relationship when compared to thearrangement of the downcomer units arranged along a periphery of avertically adjacent chamber.

In a further embodiment the feed liquid inlet is configured to receive aliquid selected from the group consisting g sea water, brackish water,flowback water, water produced during an oil or gas extraction, ormixtures thereof.

In a further embodiment, the carrier gas inlet is configured to receivea carrier gas selected from the group comprising air, nitrogen, oxygen,hydrogen, argon, carbon dioxide, or mixtures thereof.

In a further embodiment, the operation of the bubble column humidifierapparatus wherein the multi-stage arrangement allows for mass and heattransfer from the liquid stream to the air stream via the formation oftwo counter-flow streams.

In a further embodiment the multi-stage bubble column humidificationapparatus for use in a water de-salinization or water purificationsystem.

In a further embodiment the water gate is cylindrical, or cuboidal inshape.

In a further embodiment the funnel is conical or cylindrical in shape.

In a further embodiment the funnel is configured so as to have adiameter of 1.5 to 5 times greater than a water gate configured to havea diameter.

In a further embodiment the varying of said water gate height or lengthranges from 0.1 cm to 10.0 cm.

In a second embodiment, a method of humidifying a gas by mass andtemperature transfer from a liquid stream to a gas stream via theformation of two cross-flow streams comprising:

-   -   feeding the feed liquid stream comprising a vaporizable        component into an uppermost distal chamber of a multi-stage        humidifier through a water gate conduit housed in a base cup        downcomer to form a distal-stage feed liquid bath at a third        humidification temperature, wherein the multi-stage humidifier        comprises a vessel comprising a plurality of vertically spaced        horizontally placed porous structures defining vertical        chambers;    -   feeding a first remnant of the feed liquid from the uppermost        distal chamber into a mid-chamber of the multi-stage humidifier        through a downcomer apparatus to form a mid-stage bath at a        second humidification temperature, wherein the second        humidification temperature is lower than the third        humidification temperature, and further wherein said downcomer        apparatus comprises a funnel, a water gate, and a base cup        downcomer;    -   feeding a second remnant of the feed liquid from the mid-stage        bath into a lowermost proximal chamber of the multi-stage        humidifier through a downcomer apparatus to form a        proximal-stage bath at a first humidification temperature,        wherein the first humidification temperature is lower than the        second humidification temperature, and further wherein said        downcomer apparatus comprises a funnel, a water gate, and a base        cup downcomer;    -   siphoning a third remnant of the feed liquid from the lowermost        proximal chamber through a liquid remnant outlet so as to assure        that no gas is included in said third remnant;    -   introducing the gas through a gas inlet into the lowermost        proximal chamber at a point above the lowermost proximal-stage        bath;    -   directing the gas directly from the lowermost proximal chamber        through the porous structure into the mid-stage bath of the        mid-chamber and bubbling the gas through the feed liquid remnant        in the mid-stage bath, where the gas collects the vaporizable        component in vapor form from the second remnant of the feed        liquid to partially humidify the gas with the vaporizable        component;    -   separating the mid-stage bath from the distal-stage bath by a        top gas region in the mid-chamber filled with the partially        humidified gas from the bubbling in the mid-stage bath prior to        directing the partially humidified gas directly from the        mid-chamber through the porous structure into the distal-stage        bath of the uppermost distal chamber and bubbling the carrier        gas through the distal-stage bath, where the carrier gas        collects more of the vaporizable component in vapor form from        the feed liquid to further humidify the carrier gas with the        vaporizable component;

and

removing the humidified gas through a gas outlet from the distal-stagehumidifier chamber.

In a further embodiment, the method further comprises condensing thevaporizable component from the humidified gas in a dehumidifier afterthe humidified gas is removed from the distal chamber.

In a further embodiment, wherein the removed humidified gas, whenexiting the distal chamber, has a temperature 20° C.-30° C. higher thanthe temperature of a gas leaving the proximal chamber.

In a further embodiment, the gas is selected from the group comprisingair, nitrogen, oxygen, hydrogen, argon, carbon dioxide, or mixturesthereof.

In a further embodiment the vaporizable component is water.

In a further embodiment the feed liquid is selected from the groupcomprising sea water, brackish water, flowback water, water producedfrom oil or gas extraction, and mixtures thereof.

In a further embodiment, the method for water de-salinization or waterpurification.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows a three-stage bubble humidifier with a series of assembleddowncomer units.

FIG. 2 shows a representation of a humidification system.

FIG. 3a shows an assembled downcomer unit installed in a mid-portion ofa multi-stage bubble column humidifier and a porous structure comprisingperforations.

FIG. 3b shows a top portion of the uppermost distal chamber of the multistage bubble column humidifier apparatus.

FIG. 3c shows a base portion of the lowermost proximal chamber of themulti stage bubble column humidifier apparatus.

FIG. 4 shows a relationship between the humidifier's effectiveness andthe Gain-Output-Ratio (GOR) of the Humidification DehumidificationDesalination (HDH) system.

FIG. 5 shows a comparison between a bubble column humidifier asdisclosed herein and that of a packed bed humidifier.

FIGS. 6a, b, and c show three variations in the design of a porousstructure comprising a sparger.

FIG. 7 shows a base cup downcomer holder comprising an embedded O-ring.

FIG. 8 shows a watergate holder comprising an embedded O-ring.

FIG. 9 shows a cross section of the porous structure's openingsconfigured in a nozzle-like formation.

FIG. 10 shows an embedded O-ring around a porous structure so as to sealit within the external shell defining an interior region of themulti-stage bubble column humidifier.

FIG. 11 shows an approximate amount of bubble flow, or foam formation,at V_(SG)=25 cm/s and h=5 cm.

FIG. 12 shows an approximate amount of bubble flow, or foam formation,at V_(SG)=15 cm/s and h=5 cm.

FIGS. 13 a, b, and c show the effects that the water gate height has onthe mass flow ratio effectiveness.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The terms, first, second, third, etc., may be used herein to distinguishone element from another. Thus, a first element, discussed below, couldbe termed a second element without departing from the teachings of theexemplary embodiments.

Spatially relative terms, such as “above,” “below,” “left,” “right,” “infront,” “behind,” and the like, may be used herein for ease ofdescription to describe the relationship of one element to anotherelement, as illustrated in the figures. It will be understood that thespatially relative terms, as well as the illustrated configurations, areintended to encompass different orientations of the apparatus in use oroperation in addition to the orientations described herein and depictedin the figures.

Further still, in this disclosure, when an element is referred to asbeing “on,” “connected to” “flush with” or “coupled to” another element,it may be directly on, connected or coupled to the other element orintervening elements may be present unless otherwise specified.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of exemplary embodiments.As used herein, singular forms, such as “a” and “an,” are intended toinclude the plural forms as well, unless the context indicatesotherwise. Additionally, the terms, “includes,” “including,” “comprises”and “comprising,” specify the presence of the stated elements or stepsbut do not preclude the presence or addition of one or more otherelements or steps.

Furthermore, the dimensions of the multi-stage bubble column humidifier,as well as its individual components, presented herein are not intendedto limit the scope of other embodiments, nor are the given pressure orair velocity rates to be seen as limiting to other embodiments.Embodiments comprising specific dimensions are not intended to limit alarger scale version of the same apparatus.

A downcomer apparatus for use in a vapor-liquid contact apparatus andthe operation thereof is described herein. Various embodiments of theapparatus and methods may include some or all of the elements, featuresand steps described below.

A downcomer apparatus, as assembled, for use in a vapor-liquid contactapparatus such as, but not limited to, a multi-stage bubble-columnhumidifier and a contact tray apparatus. The humidifier, configured soas to efficiently humidify dry air, can be used as an integral part of alarger humidification-dehumidification system, while the contact trayapparatus, configured so as to efficiently carry out chemicalprocessing, may also be used in a larger-scale operation. The bubblecolumn humidifier as disclosed herein provides advantages over the priorart packed-bed heat exchanger in terms of a reduced cost, as both theequipment cost and the cost of energy for operation can be decreased.For example, the high heat and mass transfer rate between a liquid and agas in the multi-stage bubble column humidifier enables a small design,and furthermore, the energy for the humidification process can bedirectly provided by the feed liquid in the humidification chambers.

The multi-stage bubble column humidifier apparatus as described hereincan be used to separate pure water from a feed liquid comprising, butnot limited to, seawater, brackish water and waste water. Waste watercan include, but is not limited to, flowback water and water producedfrom oil or gas extraction/production processes. Furthermore, themulti-stage humidifier is not only able to produce fresh water, but toconcurrently concentrate the volume of a waste or brine stream,resulting in a reduction of pollution, contamination, and remediationcosts.

Both the contact tray apparatus and the multi-stage bubble columnhumidifier apparatus as disclosed herein have an external shell definingan interior region for carrying out a cross flow mass and temperaturetransfer process. The external shell comprises a column, an upper plateand a lower plate. Within this shell, the apparatus has a plurality ofhorizontal porous structures defining vertical chambers within theinterior region. The horizontally-placed porous structures, sometimesreferred to herein as stages, support a vapor, liquid, or vapor-liquidmixture thereon, wherein the porous structures, such as a sieve plate orsparger, comprises a plurality of openings allowing for the upwardpassage of a vapor or gas. In one embodiment, the chambers each have awidth, defined by the external shell, measured horizontally, and aheight, defined by the external shell, measured vertically, where thewidth is at least twice as great as the height. The apparatus also has acarrier gas inlet; a carrier gas outlet, a liquid remnant outletcomprising a discharge siphon system; a feed liquid inlet; and a seriesof downcomer units wherein each pair of vertically adjacent chambers isin liquid communication via at least one downcomer unit. Notably, thedowncomer unit is the sole conduit configured for providing liquidcommunication between two adjacent chambers.

The vertical chambers within the interior region of the humidifierapparatus comprise at least a lowermost proximal chamber, an uppermostdistal chamber, and at least one mid-chamber between the proximal anddistal chambers. The lowermost proximal chamber comprises the carriergas inlet and the liquid remnant outlet housed in the lower plate, whilethe uppermost distal chamber comprises the feed liquid inlet and thecarrier gas outlet housed in the upper plate. The inlets and outlets areheld within the upper and lower plates by means of O-rings, however theycould also be held by other means including, but not limited tothreading within the plates. Additionally, the inlets and outlets couldalso be manufactured into the plates.

Each of the downcomer units comprises a funnel, a watergate and a basecup downcomer. A lower portion of the watergate is seated in the basecup and is sealed therein using an embedded O-ring. An upper portion ofthe watergate is coupled with the funnel, and this attachment is alsosecured using an O-ring. In an alternate embodiment, these componentscan be coupled during the manufacturing process.

The downcomer unit is positioned within a vapor-liquid contactapparatus, such as a humidifier, with the funnel portion of thedowncomer unit located in one chamber, and the base cup downcomerembedded in either the porous structure, or the external shell (in thecase of the lowermost proximal chamber) of an adjacent underlyingchamber. The water gate portion forms a conduit from the funnel to thebase cup downcomer so as to form a pathway for liquid flowing from theone chamber to an adjacent underlying chamber. The humidifier'slowermost proximal chamber, which lacks an adjacent underlying chamber,does not have the funnel portion of the downcomer unit positionedtherein.

The downcomer unit is furthermore arranged within the apparatus in aperipheral and offset, or juxtaposed pattern. This offset, or juxtaposedrelationship, is determined by alternating the placement of the base cupdowncomer of the downcomer unit between pairs of vertically adjacentchambers. This applies to all of the chambers held in series. Forexample, when viewed from the top of the humidifier apparatus, theplacement of one of the base cup downcomer units occurs at 180°±5° ofthe placement of the base cup downcomer of both the overlying andunderlying vertically adjacent chambers. If more than one downcomer unitis necessitated in each chamber for liquid communication, the placementof the base cup downcomer will again be offset. For example, having twobase cup downcomers placed at 180°±5° of each other in one chamberresults in the juxtaposed placement of two base cup downcomers ofdowncomer units of an overlying or underlying adjacent chamber to bepositioned at 90°±5° with respect to the two base cups arranged in theone chamber.

The design of the downcomer unit as a whole improves the structuralsupport of the humidifier vessel, especially in those embodiments wherethe apparatus comprises more than four chambers, or has larger diameterdesigns with moderate to low stage, or porous structure spacing.Furthermore, a peripheral placement of the downcomer apparatus avoidsthe performance degrading effect of depositing the liquid in the centerof the chamber where froth formation originates, and could subsequentlybe disrupted by the turbulent input of the liquid flow. It also allowsfor the greatest porous area on each stage so as to help achieve thedesired level of foam formation. Of further note is the simplificationin controlling the water level in each chamber that these units provide.

Advantageously, the downcomer unit is not irreversibly attached to theexternal shell of the apparatus, thus allowing for ease of exchange orrepair of the individual components making up the downcomer unit itself.Most notably, as both the funnel and the watergate of the downcomer unitare not contiguous with the external shell of the multi-stage bubblecolumn humidifier, this allows for even greater freedom in the repair orreplacement of these components. Similarly, the porous structure is alsoeasily removable, either for repair, cleaning, or replacement, due tothe fact that it is also not contiguous with the external shell of thehumidifier. As the design and use of the downcomer unit as disclosedherein also minimizes the risk of fouling, or plugging, of the openingsof the porous structure, such as a sparger, any removal of the porousstructure for cleaning will be minimal.

The bubble column humidifier apparatus itself comprises an insulatingcasing material. A loss of heat to the surrounding area reduces thepotential of heat transfer between a liquid stream and a carrier gas,and this would consequently reduce the effectiveness of a humidifiersystem. Casing material may be selected from the group consisting of,but not limited to, metal, plastic, thermoplastics, (i.e. chlorinatedpolyvinyl chloride (CPVC)), and expanded polyethylene and mixturesthereof. In a preferred embodiment the material is an expandedpolyethylene with a thermal conductivity of 0.020 W/mK-0.050 W/mK,preferably 0.030 W/mK-0.040 W/mK, most preferably 0.035-0.039 W/mK.

The apparatus is provided with an opening through which enters a coolinggas, or air, forced into the apparatus by a blower such as, but notlimited to, a centrifugal blower operated by an electric motor in aconventional manner. This gas is directed upwards and through at leasttwo porous structures installed in a vertically spaced horizontal mannerso as to define at least three chambers within the multi-stage bubblecolumn humidifier. In one embodiment, the air enters the bubble columnhumidifier at an ambient temperature and humidity, and is passed, orsparged through a porous structure, such as a sparger to form bubbles ina bath of a heated liquid, such as water. In this direct contactprocess, mass and heat are transferred simultaneously from the hot,heated water to the inherently cooler air bubbles. Then, the humid airmoves upward through the overlying chambers held in series, in the samemanner until reaching the carrier gas outlet. The gas is furthermoresupplied at a pressure sufficient to overcome the hydrostatic heat ofthe liquid. As air is a much poorer conductor of heat than water, due inpart to the low density of this gas (approx. 1/900^(th) that of water),the creation of bubbles, or thin films of air, results in the creationof a highly effective heat transfer system. This heat transfer system ismuch more efficient when compared to previous systems which created finedroplets of thin films of water.

As previously stated, the dimensions presented in the followingembodiments are not intended to limit the scope of this disclosure.

In one embodiment, the height of each chamber of the multi-stage bubblecolumn humidifier is 20 cm±1 cm, the height of each of the base cupdowncomers, as well as the height of the funnel and watergate portionsrising above the porous structure, is 1-5 cm. The width of each of thebase cup downcomers is 42±5 mm and the width of the watergate is 21±5mm. The porous structure of a vapor-liquid contact apparatus, such as amulti-stage bubble humidifier, is installed so that it forms adjacent,or subsequent, chambers within the vessel, otherwise defined as anexternal shell defining an interior region. It may be made of anypractical material such as, but not limited to, metal, plastic,thermoplastics; (i.e. chlorinated polyvinyl chloride (CPVC)), andexpanded polyethylene. In one embodiment the porous structure is asparger having a diameter of 277±10 mm and a width of 17±5 mm,comprising a lower surface and an upper surface, wherein each surfacecomprises a number of openings. These openings may vary, or beconsistent in their diameter throughout their respective surfaces, so asto produce bubbles of gas, also varying or set in diameter. In apreferred embodiment, the openings, or pores, located on the uppersurface of the porous structure, are smaller in diameter as compared totheir respective openings, or pores, located on the lower surface. Theopenings may comprise 0.1 to 15 percent of the total upper surface area;more preferably, the openings may comprise 0.5 to 10 percent of thetotal upper surface total area; most preferably, said holes may equal intotal area 0.6 to 5.0 percent of the total upper surface area.

The type of porous structure utilized in the bubble column humidifier isdependent on a number of variables such as, but not limited to, thedesired air bubble size and the desired air bubble amount. In oneembodiment, it is desirable to obtain bubbles, or froth of a smalldiameter ranging from, 0.05 mm-5 mm, preferably 0.50 mm-2.5 mm, mostpreferably 0.75 mm-1.0 mm in diameter so as to speed up mass and heattransfer reaction rates and save valuable processing time. A finernozzle pore (opening) size is used to prevent any liquid frompenetrating back into the pores at a lower internal pressure and assurethat all liquid passes through their respective water gate(s) to anadjacent chamber below. The integrity of the porous structure isimportant. The porous structure(s) chosen herein for the bubblehumidifier are designed to perform well under conditions involving highheat and pressure. The size of the openings, along with the diameter andthe thickness of the porous structure itself, are two of the criteriaused to select the best porous structure chosen to withstand theseconditions without cracking or breaking so as to assure that theefficiency of humidifier remains high. Also, the composition of the feedliquid will influence the selection of the porous structure due to theamount and particle size of any solids found in the feed liquid stream.In this disclosure, the porous surface area of the porous structure waschosen so as to assure the integrity of the porous structure. That is,the porous structure is configured so as to provide integrity and,additionally, a lesser chance of becoming fouled. Specific porousstructures may be selected from the group consisting of, but not limitedto, sieve plates, radical spargers, ring spargers, spider spargers andwheel-type spargers each comprising openings, or pores, for the passageof a carrier gas therethrough.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views

As seen in FIG. 9, the porous structure openings 130 may range indiameter from 0.5 mm to 5.0 mm, preferably 1.0 mm to 3.5 mm, mostpreferably 1.7 mm to 2.2 mm on the upper surface, with correlatingopenings on the lower surface having a diameter of for example 2.5× thatof the upper surface diameter. In a preferred embodiment, when the crosssection of the sparger 98 is viewed, the opening remains at the largerof the diameters for the majority of the length of the opening, asmeasured from the upper surface of the sparger to the lower surface ofthe sparger. In a most preferred embodiment, the sparger measures 17±2mm from the lower surface to the upper surface, and comprises openingsof 5.0 mm as measured from the lower surface to 2 mm below the uppersurface; at this point the openings narrow to 2.0 mm so as to form a‘nozzle’-like structure. It is also within the scope of this disclosureto vary the size of the perforations in the porous structure, such as asparger, so that within the structure itself some openings are greaterin diameter than others. In one embodiment, a sparger comprising largerdiameter opening ranging from 2.2 mm-5.0 mms, either on its lower,upper, or both surfaces define some chambers, while other porousstructures comprising smaller diameter openings define other chamberswithin the same humidifier vessel. These variations in pore size mayassist in maintaining desired air pressures and water levels within themulti-stage bubble column humidifier. Furthermore, the diameters of theopening may be altered by the inclusion of a ‘sliding plate’ so as toreduce the size of the pores, or by changing the sparger completely.

It is desired that the bubble component generated by the porousstructure forms ‘froth’. This froth commonly forms in a bubble columnhumidifier at a location where air bubbles are dispersed throughout thewater. The level of froth formation must be closely monitored, asalthough this foam increases the surface area so as to increase the rateof transfer, it will also hamper the efficiency of the apparatus, suchas the humidifier, due to the propensity of the bubble, or foamcomponent to re-enter an adjacent underlying chamber. The two mainfactors causing the foam formation in the multi-stage bubble columnhumidifier as disclosed herein are the air superficial velocity and thewater gate height.

Advantageously, the water gate height of the downcomer unit as disclosedherein may be changed out quickly. This is due in part to the use of anO-ring as a means of sealing the watergate within both the porousstructure and the base cup downcomer. If a high level of liquid isnecessitated in a chamber, this will increase the probability of theliquid ‘backing up’ in the watergate so as to re-enter the bath fromwhere it originated. This back-up can be avoided by installing awatergate with a longer, more appropriate length. The watergate may alsobe changed, or adjusted, so to place the funnel portion at a height soas to further restrict a bubble component from entering into said watergate.

Furthermore, the funnel, of the downcomer unit is configured so as toform a ‘lip’, or weir. This configuration assures that bubbles carryingboth gas and an evaporated liquid such as steam (a vaporizable componentof one embodiment wherein the feed liquid is water), are excluded fromentering the water gate and travelling downwardly and re-entering achamber that it had already occupied. As there is a lesser gas componentre-circulating, a greater efficiency in mass and temperature transfer isachieved. In one embodiment, the funnel comprises a cylindrical orconical shape. The funnel may vary in circumference to account for thevariations in a bubble, or froth components' amount and size. In apreferred embodiment, the diameter of a funnel, at its widestcircumference, is 1 to 10 times that of a diameter of a water gate towhich it is coupled. In a most preferred embodiment, the diameter of thefunnel at its widest circumference is 1.5 to 5 times that of thediameter of the water gate to which it is coupled.

The design of the base cup downcomer is key in preventing the fouling ofthe sparger. This is accomplished by securing the base cup downcomer tothe porous structure at the bottom of a lower vertically adjacentchamber so as to initially receive the remnant fluid from a precedingadjacent overlying chamber. The design of the base cup allows for thesettling of any sediment inside the cup, rather than on the pores of theporous structure. The base cup downcomer design has the additionalintent of slow the outflowing of fluid from the water gate so as toprovide a substantially uniform distribution of liquid to a bath formingin a chamber. The turbulence of the outflowing fluid may be furthermodified with any changes in length or width of the watergate so as toinfluence laminar flow throughout the conduit. By varying the length, orwidth, a greater or lesser amount of foam formation and/or foamdampening will occur, thus further providing means to regulate foamformation and increase humidifier efficiency.

Further still, it is within the scope of this disclosure to carry out amulti-extraction process, wherein a remnant liquid removed via a siphonsystem of one multi-stage bubble humidifier apparatus now becomes theinput feed liquid of a secondary multi-stage bubble humidifier apparatusso as to further increase heat and mass exchange.

The multi-stage bubble column humidifier as disclosed herein has aseries of downcomer units wherein each pair of vertically adjacentchambers is in liquid communication via a downcomer unit. FIG. 3aillustrates the arrangement of a funnel 87 water gate 88 and base cupdowncomer 89, so as to form a downcomer unit 40 in a mid-chamber 114 ofa multi-chamber bubble column humidifier. This arrangement providesliquid communication between adjacent vertical chambers. The bottomportion of the water gate 88 is installed in the base cup downcomer 89so as to force a gas, or air stream, through to an overlying adjacentchamber via the bubble distributor, or sparger, holes 130 instead of viathe water gate 88. An upper portion of the water gate 88 and connectswith a cylindrical or conical funnel 87 seated flush on top. The basecup 89 is secured to the bottom of mid-chamber 114 in a porous structure97, such as a sparger. FIG. 3b shows a portion of the uppermost distalchamber 118 of a multi-stage bubble humidifier apparatus comprising anupper plate 106 of the external shell 84, a carrier gas outlet 104, anda feed liquid inlet 100. FIG. 3c shows a portion of the lowermostproximal chamber 112 of the multi-stage bubble humidifier 82 comprisinga lower plate 108 of the external shell, 84, a carrier gas inlet 96, aliquid remnant outlet 94, said outlet further comprising a dischargesiphon system (not shown), and a base cup downcomer 92 holding watergate 91 therein.

The dimensions presented in the following embodiments are not intendedto limit the scope of other embodiments, nor are the given pressure orair velocity rates to be seen as limiting to other embodiments.

In one embodiment, the humidifier comprises a cylindrical column with aheight of 1.5 m±10 cm and a diameter of 0.25 m±5 cm, having an upperplate, and a lower plate fixed to the column so as to create an externalshell defining an interior opening. At least one sparger, havingopenings configured so as to form a nozzle, is placed horizontallywithin the vessel so as to form vertical chambers therein. Operationalparameters of this humidifier process include a watergate height of 1cm-5 cm and a gas superficial velocity greater than or equal to 20cm/sec, preferably greater than 30 cm/sec, most preferably greater than35 cm/sec. FIG. 11, is a representation of the amount of foam that canform in a chamber when the humidifier is operated within theseparameters. The resultant foam is approximately 11±2 cm, whichoverwhelms any downcomer unit held in the chamber(s). FIG. 12 is arepresentation of the amount of foam that can form in a chamber when thehumidifier is operated within the parameters of a watergate height of 5cm and a gas superficial velocity of less than 20 cm/sec. The resultsindicate that very little to no foam formation occurs, and it does notoverwhelm any downcomer unit held in the chamber(s). This is attributedto water accumulating over the sparger to a greater extent than before.

Nevertheless, if the water gate height is reduced to less than 2.6 cm,foaming will occur at a superficial velocity of 15 cm/s. Dependent onthe actual dimensions of the bubble humidifier, and concurrently theheight of the foam, the water gate height may be adjusted, or changed,in order to either increase its length or decrease its length by 0.50cm-100 cm, preferably 0.75 cm to 50 cm, most preferably 1.0 cm-10.0 cm.The use of an O-ring seal allows for any adjustments to take placequickly, and with little effort. In one embodiment, the water gate maybe exchanged out, or replaced, entirely, while in a further embodiment,the water gate comprises an adjustable, telescoping design. Generally,if the water gate height is doubled from an initial value, the airvelocity should also increase by a factor of 1.5 so as to achieve foamformation. FIGS. 13a, b, and c shows the effect of the water gate heightat different mass ratios on the humidifier's effectiveness. Thefollowing boundary conditions exist for FIGS. 13 a, b, and c:Temperature_(a,i)=34.2° C., Ø_(a,i)=55%, T_(w,i)=63.1° C.; P=101.3 kPa;single-stage. If the bubble column humidifier is operated at arelatively high air superficial velocity, the humidifier is slightlyaffected by the height of the water gate as shown in FIG. 13a whereinV_(SG)=25 cm/s and FIG. 13b wherein V_(SG)=20 cm/s. At these twosuperficial velocities, foam is formed in the bubble column whichincreases the height of the water level and the gas holdup [U. ParasuVeera, K. L. Kataria, and J. B. Joshi, “Effect of superficial gasvelocity on gas hold-up profiles in foaming liquids in bubble columnreactors” Chemical Engineering Journal; 99.1 2004, pp 53-58.Incorporated herein by reference in its entirety.] Therefore, with ahigher water level, the time and surface of contact are increasedenhancing heat and mass transfer. However, at low air superficialvelocity, there is a drop in the effectiveness at a height of 5 cm asshown in FIG. 13c since in this case there is no foam formation.Therefore, this illustrates that foam is desired so as to increase theheat and mass transfer, but it is not desired for the bubbles, or foamitself, to enter into the water gate so as to allow the air component tore-enter an originating or preceding chamber.

A multi-stage bubble-column humidifier apparatus 82 with three chambers118, 114, 112 is illustrated FIG. 1. The apparatus comprises an externalshell 84 defining an interior region and a plurality of horizontalporous structures 97, 98 defining vertical chambers 118, 114, 112 withinthe interior region. In further embodiments, more or fewerhumidification chambers can be joined, or linked in series, as describedbelow, for carrying out the humidification process. FIG. 1 alsoillustrates how a liquid 46 and a gas 48 stream achieve a cross-currentflow within the bubble column humidifier apparatus so as to carry out ahumidification process to humidify a gas stream. This process, as wellas the components of the humidifier, are outlined below:

A feed liquid 46 containing dissolved components is fed from afeed-liquid source, including, but not limited to, an ocean, pond,storage tank, or tap into an uppermost, distal chamber 118 of thehumidifier 82, via a feed liquid inlet 100 having a lowermost portionhoused in a downcomer 102 wherein the feed liquid 46 forms a bath 30contained within the chamber 118. An upper most plate of the externalshell 106 defines the top of the humidifier vessel 82, and holds anupper- to mid-portion of the feed liquid inlet 100 sealed within anuppermost portion of the external shell 106. In a first embodiment, thefeed liquid 46 is fed into the distal chamber 118 and a vaporizablecomponent, such as water, of the feed liquid 46 is vaporized into acarrier gas 48 that bubbles 94 through the bath 30, as further describedbelow. As the base cup downcomer 102 housing the lowermost portion ofthe feed liquid inlet 100 overfills its capacity, the liquid 46 overflows the base cup 102 and flows over a porous structure 98 until theliquid 46 level forming the liquid bath 30 rises so as to reach and flowinto an uppermost portion of a downcomer unit 40 comprising a conical orcylindrical funnel 87 so as to be collected therein. The funnel 87 has alip, or weir, configured so as to allow liquid to enter, but restrictthe entrance of any vapor or gas, in the form of a bubble 94, foam orfroth component, from entering into watergate 88 of downcomer unit 40and re-entering mid-chamber 114, a chamber that the vapor, or gas hadpreviously occupied. The first feed liquid remnant that is able tobreach the weir formed by the funnel 87 is now conducted, via watergate88 to a base cup downcomer 89. As base cup downcomer 89, housing alowermost portion of watergate 88, overfills its capacity, the liquid 46over flows the base cup 89 and flows over a second porous structure 97forming a mid-chamber bath 34. This bath 34 continues to rise until theliquid 46 level forming the liquid bath 34 reaches and flows into anuppermost portion of a downcomer unit 42 comprising a conical orcylindrical funnel 90 so as to be collected therein. The funnel 90 isalso configured so as to form a lip or weir to restrict the entrance ofany vapor or gas, in the form of a bubble 94, foam or froth component,into a watergate 91, but to allow a second, more concentrated remnant ofthe feed liquid 46 comprising further-concentrated dissolved componentsto be fed from the mid chamber 114 via downcomer apparatus 42 in thesame manner as described above, into a lowermost proximal chamber 112,in which the second remnant of the feed liquid 46 forms another bath 36.A lowermost portion of the external shell 106 holds a mid-portion of thecarrier gas inlet 96 sealed within. Although the carrier gas 48 entershumidification chamber 112 via carrier gas inlet 96, the carrier gas 48is released above the level of the second remnant liquid bath 36 and nobubble 94 formation occurs within this remnant bath 36. The remnant ofthe feed liquid 46, which can now be in the form of a cold brine, isremoved from the first-stage humidification chamber 112 via a siphonsystem conduit 94 so as to assure that no carrier gas 48 leaves with theremnant of the feed liquid 46. In one embodiment, the remnant of thefeed liquid 46 is removed to an area such as a brine storage reservoir,while in an alternative embodiment the remnant liquid enters a secondarymulti-stage bubble humidifier vessel 82 via a secondary water inletwater gate 99 so as to undergo further mass and temperature cross flowtransfer and concentration.

The temperature of the feed liquid is reduced from chamber-to-chamber,in part, via the energy used for vaporization of the vaporizablecomponent from the feed liquid at each stage into the carrier gas.Accordingly, the temperature of the feed liquid can drop byapproximately 30% to 50% across each stage; preferably 35% to 45%.

Prior to and concurrent with the introduction of the feed liquid 46 tothe bubble humidifier apparatus 82, a cool, dry carrier gas 48 isintroduced to humidification chamber 112, and subsequently flows throughthe humidifier vessel 82 from chamber to chamber so as to flow from 112to 114; and 114 to 118 prior to exiting the uppermost distal chamber 118via a carrier gas outlet gate 104. The flow of the carrier gas 48 withinthe chambers, as well as within the multi-stage bubble humidifier as awhole, is illustrated with arrows 110. The carrier gas 48 can beselected from the group consisting of, but not limited to, ambient air,carbon dioxide, hydrogen, argon, nitrogen, oxygen, and/or mixturesthereof. The chosen carrier gas 48 can initially be fed into thelowermost proximal chamber 112 via a pressurized air blower pump feedinginto a carrier gas inlet, or reservoir 96 sealed within the lowermostportion of the external shell 106. The carrier gas 48 fills a gas region120 inside the lowermost proximal chamber 112 and flows through a porousstructure, 97, such as a sparger, into the bath 34 of the mid-chamber114 in the form of bubbles 94. It is within this bath 34 wherein thecarrier gas 48 is heated and humidified with the heat and humidificationprovided by the feed liquid 46. The vaporizable component, such aswater, of the feed liquid 46 vaporizes into the bubbles 94 at thegas-liquid interface of the bath 34 and bubbles 92. The bubbles 92 flowup through the bath 34, gaining thermal energy and also acquiring avaporizable component (in vapor form) from the bath 34 until the carriergas 48 enters the top gas region 121 above the bath 34 and proceedsthrough the porous structure 98 into the bath 30 of the uppermost distalchamber 118 in the form of bubbles 94. It is within this bath 30 whereinthe carrier gas 48 is further heated and humidified with the heat andhumidification provided by the feed liquid 46. A second vaporizablecomponent, such as water, of the feed liquid 46 vaporizes into thebubbles 94 at the gas-liquid interface of the bath 30 and bubbles 94. Aspreviously, the bubbles 94 flow up through the bath 30, gaining thermalenergy and also acquiring a vaporizable component (in vapor form) fromthe bath 30 until the carrier gas 48 enters the top gas region 123 abovethe bath 30 and proceeds through a carrier gas outlet 104. The nowhumidified gas, upon exiting the uppermost proximal chamber, has atemperature 20° C.-30° C. higher than when it entered the lowermostdistal chamber. It may be collected, or flow into the atmosphere. Ifcollected, it may be subjected to dehumidification in a dehumidifier, aspart of a HDH-desalinization system.

It should be noted that porous structures 97, 98 comprise a multiplicityof perforations 130 configured so as to provide ‘nozzle’ openings. Theseopenings pass the carrier gas 48 upwardly through their respectivechambers at a desired pressure and velocity. Also, in terms of liquidflow-through, or weeping, if a pressure drop occurs on the carrier-gas(bottom) side of the bubble generator 98 the liquid has a highprobability of weeping. This is due to the fact that pressure is astrong function of the height of the bath 30, 34 since the hydrostaticheight of the bath 30, 34 needs to be overcome by the gas 48 to keep thebath liquid from “weeping” through the porous structure 98 to anunderlying chamber. One advantage to maintaining the low height of eachof the baths is the reduced electricity consumption by a gas-movingdevice (blower) due to the decreased pressure drop. Maintaining the lowheight of the baths 30 and 34 is feasible in this context because thecharacteristic dimension of heat transfer is of the order of a fewmillimeters.

In a preferred embodiment, chambers formed in accordance with thisdisclosure comprise downcomer units peripherally arranged around saidporous structure so that the funnels and downcomers of adjacent orsequential overlying or underlying chambers are aligned at 180°+/−5° ofeach other as illustrated in FIGS. 1, 2, and 3 a. This juxtaposedpositioning, along with the peripheral arrangement is preferred in orderto off-set any turbulence which might be created when liquid 46 flowingout of the downcomer 86 enters into a forming bath 30, 34, 36. The sideor peripheral placement also maximizes the area available for bubbledistribution. It should be understood that downcomer apparatuses 40 and44 are defined herein so as to show their juxtaposed andstage/chamber-specific location in said multi-stage bubble columnhumidifier, however, the downcomer apparatuses have the same componentsand design and may be used interchangeably as desired. In a furtherembodiment, more than one downcomer apparatus may be installed in eachchamber, so that they are 90°+/−5° from each other and offset 90°+/−5°from those downcomer units in liquid communication with an adjacentoverlying or underlying chamber.

FIG. 2 shows a schematic diagram of a humidification system. The systemincludes an air blower 50, an instant water heater 80, and a multi-stagebubble column humidifier vessel 82. A stream of air 48 is delivered tothe bubble column humidifier 82 by an air blower 50. In a most preferredembodiment, an 800 W blower with a maximum volumetric flow rate of 4.5m³/min is used. The air 48 is humidified and heated up in the bubblecolumn humidifier 82 by direct contact with a water stream 46, thenleaves from outlet gate 104. The liquid stream 46 is supplied to theentrance of water gate 99 either directly from a source such as a sea,ocean, ground water, wastewater, or other body of water, or by pumpingfrom a tank holding said source, through a liquid feed conduit such as a½″ CPVC pipe (not shown). The water stream 46 undergoes prior heatingusing an instant water heater 80. In a most preferred embodiment, theheater has a maximum power of 7.5 kW and is optionally supported by aproportional-integral-derivative controller (PID controller) (not shown)in order to provide a constant temperature for the water stream 46. Thelevel of the bath of water found on each stage may be adjusted byvarying the rate of water inlet flow, and also by varying the pressureof the air flowing upwards through the bubble generators.

There are two counter-flow streams in the humidifier 82. One streamcomprises a hot saline water stream 46 and a second stream is a moistair stream 48 that comes from ambient air through an air entrance 96. Inthe humidifier 82, mass and heat are transferred simultaneously from thesaline water stream 46 to the air stream 48.

At the bottom of the humidifier vessel 82, the remnant liquid 46, suchas water leaves the humidifier 82 through a siphon system 94 so as toassure that there is no air, or gas 48 leaving with the remnant of theliquid stream 46. In one embodiment, the remnant water is a brinewherein said brine may comprise a cooler, or cold, temperature whencompared to the temperature of the initial liquid feed stream. Furtherto this, a multi-extraction process using the apparatus and methodsherein may be used to further increase heat recovery, in that theremnant water brine of one humidification process may form the feedliquid of a further humidification process.

The apparatus and process as disclosed may further comprise equipment orsteps for condensing the vaporizable component from the humidifiedcarrier gas in a dehumidifier after the humidified carrier gas isremoved from a final or second humidifier chamber. Both the humidifierand dehumidifier may be part of ahumidification-dehumidification-desalinization system for the productionof fresh water.

In determining the effectiveness of a humidifier—for use in for aHDH-system-comprising the downcomer units, several parameters need to beconsidered. Specific to the efficiency of the bubble humidifier itselfare those parameters such as, but not limited to, the air superficialvelocity, the mass flow rate ratio, the number of stages, the watergateheight, the porous structure profile, and insulation of the apparatus.Any efficiency improvement in these parameters will increase theefficiency of the humidifier, and furthermore increase the overallperformance of the HDH system as well. In order to evaluate theeffectiveness and performance of the bubble column humidifier of thisdisclosure, an energy-based effectiveness definition proposed by Narayanet al. was used. [G. Prakash Narayan, Karan H. Mistry, Mostafa H.Sharqawy, Syed M. Zubair, and John H. Lienhard, “Energy Effectiveness ofSimultaneous Heat and Mass Exchange Devices”. Frontiers in Heat and MassTransfer 1.2 (2010) pp. 1-13 Incorporated herein by reference in itsentirety.] Namely, the equation that was used to give the effectivenessof the multi-stage bubble column humidifier is: ε_(n)=1−(1−ε₁)·C^(n-1)where ε is the energy based effectiveness and C is the heat capacity.

In Table 1, the pressure losses and humidifier effectiveness are listedat different mass flow rate ratios. These data are obtained from thethree-stage bubble column humidifier at Ta,i=T₁=34.2° C.; Øa,i=Ø1=55%;Tw,i=T₁₀=63.1° C.; P=101.3 kPa; h=1 cm and VSG=25 cm/s.

TABLE 1 Experimental data for a Three-chamber Humidifier Mass flow rateratio, m r Pressure losses, P_(losses) Effectiveness, ε_(H) [—] [kPa][%] 2 0.91 87.6 4 0.91 80.0 6 0.91 88.9

Parameter Definition Value T1 temperature of air entering the system34.2° C. T10 temperature of water entering the humidifier 63.1° C. Ø1relative humidity of air entering the system 55% P_(H) humidifierpressure 101.3 kPa {dot over (m)}_(da) mass flow rate of dry air 0.1kg/s Pr compressor pressure ratio 1.5 ε_(D) dehumidifier effectiveness90% ε_(HX) heat exchanger effectiveness 85% η_(c) compressor efficiency78% η_(t) turbine efficiency 85% ΔP_(H) pressure drop across thehumidifier 0.91 kPa ΔP_(D) pressure drop across the dehumidifier 0.5 kPaΔP_(HX) pressure drop across the heat exchanger 0.5 kPa

Air superficial velocity V_(SG) is defined as the ratio of thevolumetric flow rate of the air to the cross sectional area of thebubble column (A_(column)), [Nigar Kantarci, Fahir Borak, Kutlu O.Ulgen, “Bubble column reactors” Progress Biochemistry 40.7 (2005) pp.2263-2283. A. A. Mouza, G. K. Dalakoglou, S. V. Paras “Effects of liquidproperties on the performance of bubble column reactors with fine porespargers” Chemical Engineering Science 60.5 (2005), pp. 1465-1475.Incorporated herein by reference in their entirety.], while the MassFlow Rate ratio is defined as the mass flow rate of the water stream tothe mass flow rate of the air stream.

The bubble column humidifier efficiency based on data for bubble columnsgiven in open literature, the heat-transfer coefficient in a multi-stagebubble-column condenser is estimated to be 7 kW/m2K. This heat-transfercoefficient is comparable to, if not higher than, film condensation ofsteam. The higher energy recovery can be maintained using thismulti-staging technique, thus reducing the overall cost of the system,as the energy cost and the equipment cost are both reduced. Theadvantages of the humidifier of this disclosure include a high mass andheat transfer rate within a small, compact humidifier. In addition toits high effectiveness, the design results in lowered economic costs,minimized time of fabrication, and also minimized time of installation.Of further note is the simplification in controlling the water level ineach chamber that this apparatus provides

System parameters used to evaluate the performance of the multi-stagebubble column humidifier apparatus in a humidification-dehumidification(HDH) cycle include the Gained-Output-Ratio (GOR), Vapor productivityratio (VPR), Specific heat input (SHI), Energy Effectiveness, and HeatCapacity Rate Ratio. GOR measures the performance of a thermaldesalination plant. It is defined as the ratio of the enthalpy ofvaporization of the produced water to the heat input to the system.Also, GOR is a function of two system parameters; the vapor productivityratio (VPR) and the specific heat input (SHI). VPR is defined as theratio of the produced water rate to the rate of compressed water vaporat the humidifier exit in the system. SHI is defined as the ratio of theheat input to the system to the rate of compressed water vapor at thehumidifier exit. FIG. 4 shows the relationship between the gain outputratio GOR [-] and the percentage of humidifier effectiveness (ε), i.e.the effect of the humidifier effectiveness on the GOR of the HDH system.Energy Effectiveness for adiabatic heat and mass exchange devices isdefined as the ratio of total enthalpy rate difference (Δ{dot over (H)})to the maximum possible total enthalpy rate difference (Δ{dot over(H)}_(max)). Depending on which stream has the maximum heat capacityrate, the maximum possible change in total enthalpy rate can be ofeither that of the moist air or the water stream. And, in this work, theHeat Capacity rate ratio for the heat and mass exchange devices isdefined as the ratio of the maximum possible change in the totalenthalpy rate of the cold liquid stream to the maximum possible changein the enthalpy rate of the hot liquid stream

FIG. 5 shows a comparison in effectiveness between the multi-stagebubble column humidifier and a multi-packing packed bed column carriedout by Narayan et al [G. Prakash Narayan, Maximus G. St. John, Syed M.Zubair, and John H. Lienhard V. “Thermal design of the humidificationdehumidification desalination system: An experimental investigation”.International Journal of Heat and Mass Transfer 58 (2013), pp. 740-748.Incorporated herein by reference in its entirety.] The followingboundary conditions exist for FIG. 5: Temperature_(a,i)=33° C.,θ_(a,i)=40%, T_(w,i)=60° C.; P=101.3 kPa; m_(r)=2.8. The comparison isconducted under similar conditions. The volume of each packing block inthe packed bed humidifier is 0.07 m³, whereas the volume of each stagein the multi-stage bubble column humidifier is 0.012 m³. Even with thelower volume, the multi-stage bubble column humidifier shows a highperformance when compared with the packed bed humidifier. Notably, evena three-stage bubble column humidifier has a higher effectiveness thanthat of a five-packing-block packed bed humidifier; (0.036 m³ bubblecolumn humidifier compared to a 0.35 m³ packed bed humidifier). Thistranslates to an effectiveness of 85% as compared to the 76%effectiveness achieved by the five-packing-block packed bed humidifier.Moreover, the multi-stage bubble column has lower volume, whichtranslates to a reduction in manufacturing costs.

Example 1

A humidifier having the following structural features, as well as aninsulator comprising expanded polyethylene with a thermal conductivityof 0.034 W/m·K, is operated so as to determine its efficiency:

Frame

The column of the exterior shell of the multi-stage bubble columnhumidifier is constructed out of a 277 mm±50 mm Plexiglas pipe which isa transparent thermoplastic material having a thermal conductivity of0.19 W/mK. This material allows visibility inside the column during theprocess. Also, due to its low thermal conductivity, heat losses from thesystem are minimized. Both the upper plate and the lower plate of theexterior shell are made from 18 mm±5 mm thick chlorinated polyvinylchloride (CPVC), and are fitted to the column so as to respectivelydefine the top of uppermost distal chamber and the bottom of thelowermost proximal chamber. Both plates are furthermore sealed to thecolumn by means of an embedded O-ring. The humidifier chambers may eachhave a width, measured horizontally, and a height, measured vertically,wherein the width is at least twice as great as the height for anincreased efficiency of mass and heat transfer during the cross flow ofa liquid and a gas.

Sparger

The sparger, or perforated plate, is made of a PVC sheet, 18 mm thick.Three different configurations for the sparger have been tested as shownin FIGS. 6a, b and c . These three spargers differ in their number ofholes, pitch size and open area ratio wherein the open area is the ratiobetween the total area of the holes and the total sparger area. Table 2shows the configuration parameters for each sparger.

During testing, sparger 6 c encountered efficiency issues due to a waterleakage through the boundary openings. The leakage was attributed to theshear stress encountered near the frame of the column which resulted ina lower air velocity at that location. Sparger 6 c is not considered apreferred embodiment in this disclosure. FIG. 7 shows the effect of thesparger profile on the humidifier effectiveness at different mass flowrate ratios. It can be concluded that the humidifier effectiveness issomewhat affected by the sparger profile as the effectiveness of sparger6 a is slightly higher (2.5%) than that of sparger 6 b. However,pressure losses in sparger 6 a were found to be much higher (more than400%) when compared to sparger 6 b. This is attributed to the reducednumber of holes which translates into a higher air jet velocity throughthe holes, resulting in a higher dynamic pressure loss. For this reasonsparger 6 b was selected for the testing of the downcomer apparatus.

TABLE 2 Sparger profile Sparger Sparger Hole Open area Number of sizediameter; mm diameter; mm ratio (%) holes Pitch a 277 2 0.68 130 20 b277 2 2.22 425 10 c 277 2 2.71 520 10

FIG. 9 illustrates how the openings 130 are designed in a way to reducethe dynamic pressure drop. The diameter of the holes extends 5 mm fromthe entrance, until 2 mm before the upper surface of the sparger. Then,the diameter of the hole narrows to 2 mm until the upper surface of thesparger. This forms what is termed a ‘nozzle’ of the sparger. Thesparger is fitted in the column by an embedded O-ring 124 around thesparger 98 as shown in FIG. 10. The O-ring 124 and groove design wereselected according to MARCO RUBBER & PLASTIC PRODUCTS, INC standards[Standard AS568 USA O-Ring Sizing Chart. MARCO RUBBER & PLASTICPRODUCTS, INC., Industrial Groove Design Charts. MARCO RUBBER & PLASTICPRODUCTS, INC Incorporated herein by reference in their entirety.] Bothprevention of air and water leakages between the stages, or between thestages and the surroundings, along with an ease of installation andrepair of the device is are obvious advantages provided by the O-ring.[Standard AS568 USA O-Ring Sizing Chart. MARCO RUBBER & PLASTICPRODUCTS, INC. Incorporated herein by reference in its entirety.]

FIG. 7 shows the sparger 98 furthermore includes a holder 150 for thebase cup downcomer, which is sealed using an embedded O-ring 128.

The sparger 98 also includes an opening 152 so as to hold a water gatewhich is sealed using an embedded O-ring 126 as shown in FIG. 8.Advantage of this technique allows for easier alteration and control ofthe height of the water gate, as well as an easy replacement of the basecup downcomer. Upper 106 and lower 108 plates, as well as the sparger98, are made of 18 mm thick chlorinated polyvinyl chloride (CPVC). Theyare also fitted in the bubble column using an embedded O-ring 124 asshown in FIG. 10.

Procedures

Air is initially blown into the bubble column humidifier using a blowerso as to establish an air current. This air current prevents anyuntreated water from flowing through the sparger holes to the stagebelow. If the water was designated to flow first, it would pass throughthe sparger holes. FIG. 2 shows how the volumetric flow rate of the airstream is adjusted to the desired volumetric flow rate using an orificemeter 56 and throttle valve 62 [Munteshari, O. “Multi-stage bubblecolumn humidifier for thermal Driven Mechanical CompressionHumidification Dehumidification Desalination System: Appendix A; April2014 Incorporated herein by reference in its entirety.]

After establishing a flowing air stream, the water supply valve 64 isopened. Throttle valve 62 is used to control the volumetric flow rate ofwater which is measured using a rotameter 78. The water heater 80 isturned on and set to the desired temperature. The system is observed forapproximately 30 to 60 minutes, preferably 20 to 40 minutes, mostpreferably from 15 minutes to 20 minutes in order for the system toachieve steady state conditions. While the humidification process isrunning, the valves 66, 68, 72, 74, 76, rotameter 78, and orifice meter56 are continuously monitored and readjusted to maintain a desired flowrate. At steady state conditions, the values of water temperatures atthe inlet and outlet of the water stream and air dry-bulb/wet-bulbtemperatures at the inlet, and outlet of the air stream are recordedusing a series of thermocouples 76, 70, 66, 68, 72, and 74,respectively. The value of any pressure drop in the bubble columnhumidifier 82 is recorded using a manometer 54.

Measurement Devices

K-type thermocouples were used to measure the dry and wet temperaturesof the inlet and outlet air and they were all calibrated together at thesame time using the same data logger and bath of water. Thethermocouples were all connected to a data logger with an accuracy of±0.5° C. The rotameter used for water volumetric flow rate measurementhas a range of 1-7 LPM (16.7-116.7 cm3/s) with accuracy of ±0.25 LPM(4.17 cm3/s). The pressure difference across the orifice meter and thepressure drop in the bubble column humidifier were measured using watermanometers with accuracy of ±1 mm. The approach described by Coleman andSteele [Hugh W. Coleman and W. Glenn Steele. “Experimentation,Validation, and Uncertainty Analysis for Engineers, Third Edition”.Experimentation, Validation, and Uncertainty Analysis for Engineers.John Wiley & Sons, Inc., 2009, pp. 257-269. Incorporated herein byreference in its entirety.] was performed, in order to estimate theuncertainty in the presented results. [Munteshari, O. “Multi-stageBubble Humidifier for Thermal Driven Mechanical CompressionHumidification Dehumidification Desalination System”, Thesis, King FahdUniversity of Petroleum & Minerals Apr. 7, 2014. Appendix C Incorporatedherein by reference in its entirety.] The uncertainty in themeasurements is defined as the root sum square of the bias error of theinstrumentation and the precession error observed. Accordingly, theresulting uncertainties are ±0.67 cm/s, ±0.283 kg/s, ±0.83%, ±0.85% and±2.52% in the calculated air superficial velocity, mass flow rate ratio,inlet air relative humidity, outlet air relative humidity and humidifiereffectiveness.

In describing embodiments of the invention, specific terminology is usedfor the sake of clarity. For the purpose of description, specific termsare intended to at least include technical and functional equivalentsthat operate in a similar manner to accomplish a similar result.Further, where parameters for various properties or other values arespecified herein for embodiments of the invention, those parameters orvalues can be adjusted up or down by a factor of 1, 2, 3, 4, 5, 6, 8,10, 20, 50, 100, etc., or by rounded-off approximations thereof, unlessotherwise specified. Moreover, while this invention has been shown anddescribed with references to particular embodiments thereof, thoseskilled in the art will understand that various substitutions andalterations in form and details may be made therein without departingfrom the scope of the invention. Further still, other aspects, functionsand advantages are also within the scope of the invention; and allembodiments of the invention need not necessarily achieve all of theadvantages or possess all of the characteristics described above.Additionally, steps, elements and features discussed herein inconnection with one embodiment can likewise be used in conjunction withother embodiments.

U.S. Pat. No. 8,523,985 and US 2014/0367871 are each incorporated hereinby reference in their entireties.

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, defines, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

The invention claimed is:
 1. A multi-stage bubble-column humidificationapparatus, comprising: an external shell defining an interior region; aplurality of horizontal porous structures defining pairs of adjacentvertical chambers within the interior region; a carrier gas inlet; acarrier gas outlet; a liquid remnant outlet comprising a dischargesiphon system; a feed liquid inlet; and a series of downcomer unitswherein each pair of vertically adjacent chambers is in liquidcommunication via at least one downcomer unit; wherein the verticalchambers within the interior region comprise at least a lowermostproximal chamber, an uppermost distal chamber and at least onemid-chamber between the proximal and distal chambers, the lowermostproximal chamber comprises: the carrier gas inlet; and the liquidremnant outlet, the uppermost distal chamber comprises: the feed liquidinlet; and the carrier gas outlet, each downcomer unit comprises: afunnel; a watergate; a base cup downcomer; wherein a lower portion ofthe watergate is seated in the base cup downcomer and an upper portionis coupled to the funnel.
 2. The multi-stage bubble-columnhumidification apparatus of claim 1 wherein the external shellcomprises: a column; an upper plate; and a lower plate; wherein theupper plate and the lower plate are secured to the column with anembedded O-ring.
 3. The multi-stage bubble-column humidificationapparatus of claim 1 wherein the watergate is secured within acorresponding porous structure with an embedded O-ring.
 4. Themulti-stage bubble-column humidification apparatus of claim 1 whereinthe base cup downcomer is secured to a corresponding porous structure ata bottom of the lower vertically adjacent chamber with an embeddedO-ring.
 5. The multi-stage bubble-column humidification apparatus ofclaim 1 wherein the base cup terminates at a point below a liquid levelof any of the proximal, distal or mid chambers, and is configured todistribute a liquid from the watergate in an even-flowing pattern. 6.The multi-stage bubble-column humidification apparatus of claim 1wherein the base cup is configured to collect a sediment fraction of aliquid so as to prevent or reduce a fouling of a corresponding porousstructure.
 7. The multi-stage bubble column humidification apparatus ofclaim 1 wherein the liquid remnant outlet comprises a liquid dischargesiphon system is configured so that no gas exits with remnant liquid. 8.The multi-stage bubble-column humidification apparatus of claim 1wherein in each vertical chamber, a width of each chamber is at leasttwice a height of the chamber wherein the width is defined by thehorizontal distance of the external shell, and the height is defined bythe vertical distance between adjacent porous structures.
 9. Themulti-stage bubble-column humidification apparatus of claim 1 whereinthe funnel and the watergate are not contiguous with the external shell.10. The multi-stage bubble-column humidification apparatus of claim 1wherein the watergate is capable of being configured so as to lengthenor shorten a passageway of liquid communication between the verticallyadjacent chambers.
 11. The multi-stage bubble-column humidificationapparatus of claim 1 wherein the funnel is configured to limit oreliminate entrance of a foam into a watergate.
 12. The multi-stagebubble-column humidification apparatus of claim 1 wherein each porousstructure is one selected from the group consisting of a sieve plate, aradical sparger, a ring sparger, a spider sparger, and a wheel-typesparger.
 13. The multi-stage bubble-column humidification apparatus ofclaim 1 wherein a lower surface of each of porous structure comprisesopenings of a greater diameter as compared to openings of an uppersurface of the porous structure.
 14. The multi-stage bubble-columnhumidification apparatus of claim 1 wherein the downcomer units arearranged along a periphery of the distal, mid, and proximal chambers ina vertical, offset pattern, or juxtaposed relationship.
 15. Themulti-stage bubble-column humidification apparatus of claim 1, whereinthe feed liquid inlet is configured to be connected to a liquid sourcecomprising at least one liquid selected from the group consisting of seawater, brackish water, flowback water, and water produced during an oilor gas extraction process.
 16. A method of humidifying a gas in themulti-stage bubble: column humidification apparatus of claim 1,comprising: transferring a mass and temperature from a liquid stream toa carrier gas stream via formation of two cross-flow streams comprising:feeding a liquid steam comprising a vaporizable component into anuppermost distal chamber to form a distal-stage bath at a thirdhumidification temperature; feeding a first remnant of the liquid fromthe uppermost distal chamber into a mid-stage chamber to form amid-stage bath at a second humidification temperature, wherein thesecond humidification temperature is lower than the third humidificationtemperature; feeding a second remnant of the liquid from the mid-stagechamber into a lowermost proximal chamber of the multi-stage humidifierto form a proximal-stage bath at a first humidification temperature,wherein the first humidification temperature is lower than the secondhumidification temperature; siphoning a third remnant of the feed liquidfrom the lowermost proximal chamber so as to assure that no gas isincluded in said third remnant; introducing a gas into the lowermostproximal chamber at a point above the lowermost proximal-stage bath;directing the gas directly from the lowermost proximal chamber into themid-stage bath of the mid-chamber and bubbling the gas through theliquid remnant in the mid-stage bath, where the carrier gas collects thevaporizable component in vapor form from the second remnant of the feedliquid to partially humidify the carrier gas with the vaporizablecomponent; separating the mid-stage bath from the distal-stage bath by atop gas region in the mid-chamber filled with the partially humidifiedgas from the bubbling in the mid-stage bath prior to directing thepartially humidified carrier gas directly from the mid-chamber into thedistal-stage bath of the uppermost distal chamber and bubbling the gasthrough the distal-stage bath, where the gas collects more of thevaporizable component in vapor form from the liquid to further humidifythe gas with the vaporizable component; and removing the humidified gasfrom the uppermost distal chamber.
 17. The method of claim 16, furthercomprising condensing the vaporizable component from the humidifiedcarrier gas in a dehumidifier after the humidified carrier gas isremoved from the distal chamber.
 18. The method of claim 16, wherein thevaporizable component is water.
 19. The method of claim 16, wherein theliquid stream is selected from the group consisting of sea water,brackish water, flowback water, and water produced during an oil or gasextraction process.